* Demonstration of air-fluid levels. A coconut was used to demonstrate the effect of various positions and tube angles on air-fluid levels.

(C) The cassette was at a 45º angle to the plane of the floor with the beam parallel to the air-fluid level and therefore parallel to the floor.

* Demonstration of air-fluid levels. A coconut was used to demonstrate the effect of various positions and tube angles on air-fluid levels.

(C) The cassette was at a 45º angle to the plane of the floor with the beam parallel to the air-fluid level and therefore parallel to the floor.

* Demonstration of air-fluid levels. A coconut was used to demonstrate the effect of various positions and tube angles on air-fluid levels.

(D) The cassette was at a 45º angle to the plane of the floor and therefore at a 45⁰ angle to the air-fluid level, with the beam perpendicular to the cassette. Note the central ray must be parallel to the floor to demonstrate distinct air-fluid levels.

Demonstration of air-fluid levels. A coconut was used to demonstrate the effect of various positions and tube angles on air-fluid levels.

(D) The cassette was at a 45º angle to the plane of the floor and therefore at a 45⁰ angle to the air-fluid level, with the beam perpendicular to the cassette. Note the central ray must be parallel to the floor to demonstrate distinct air-fluid levels.